Treatment string and method of use thereof

ABSTRACT

A tubular member is presented for treating a subterranean formation, the tubular member being insertable in a wellbore intersecting the subterranean formation and adapted to receive a treatment fluid under pressure. The tubular member comprises at least one assembly having at least one port; a straddle system comprising an upper packer uphole of the at least one assembly and a lower packer downhole of the at least one assembly to isolate an annular interval adjacent the ported assembly between the tubular member and the wellbore; and at least one flow diverter valve positioned uphole from the upper packer for diverting fluid from within the tubular member through an annulus between the tubular member and the wellbore to surface. Methods are further provided for treating a subteranian formation

FIELD OF THE INVENTION

The present invention relates to hydraulic or mechanical completion equipment for wellbores in general, and in particular relates to equipment for circulating fluids in fracturing and stimulating subterranean formations bearing oil or gas.

BACKGROUND OF THE INVENTION

If a hydrocarbon bearing subterranean formation either lacks permeability or flow capacity for cost effective recovery of the hydrocarbon, then it is common practice to use hydraulic fracturing or other treatment of the formation to increase the flow of the hydrocarbon, typically oil or gas. This method of stimulation creates flow channels for the hydrocarbon to escape the formation into a wellbore penetrating the formation, to maintain well production.

The wellbore typically consists of a metal pipe, commonly known as a “casing”, “production casing”, “wellbore liner” or “completion string”, which is deployed into the borehole and is cemented into place. Fracturing of the formation occurs when a treatment fluid is pumped under high pressure into the casing, usually via a tubular treatment string run inside the casing, and is ejected through holes in the casing, and through the cement, into the formation to cause fractures in its strata. The treatment fluid carries a proppant, such as sand or the like, which penetrates the fractures to hold them open after the treatment fluid pressure is released, and can include additives such as acids. Alternatively, the formatting maybe treated by injection of fluids at lower pressures than fracturing, to stimulate the formation without causing fractures in the strata.

In many fracking or treatment situations, a first treatment fluid is first pumped down the inner bore of the tubular treatment string and out through ported assemblies on the treatment string. The ported subs are preferably isolated from other stages of the formation by an isolation device to ensure that the first treatment fluid is directed to the desired zone of the formation to be stimulated. The isolation device seals against casing to prevent fluid from flowing into the annulus between the treatment string and the casing, and out of the isolated stage. In a next step, second treatment fluids are pumped down the well to frac or otherwise treat or stimulate the formation.

When the isolated zone has been treated, flow of treatment fluids is reduced or stopped entirely and the treatment string is released and moved either uphole or downhole to the next zone to be treated.

SUMMARY OF THE PRESENT INVENTION

A tubular member is presented for treating a subterranean formation, the tubular member being insertable in a wellbore intersecting the subterranean formation and adapted to receive a treatment fluid under pressure. The tubular member comprises at least one assembly having at least one port; a straddle system comprising an upper packer uphole of the at least one assembly and a lower packer downhole of the at least one assembly to isolate an annular interval adjacent the ported assembly between the tubular member and the wellbore; and at least one flow diverter valve positioned uphole from the upper packer for diverting fluid from within the tubular member through an annulus between the tubular member and the wellbore to surface.

A method is further provided for treating a subteranian formation. The method comprises inserting a tubular member into a wellbore intersecting the subterranean formation, the tubular member being adapted to receive a treatment fluid under pressure and comprising at least one ported assembly and one or more flow diverter valves positioned uphole of said ported assembly; setting an isolation device in an annulus between the tubular member and the wellbore for hydraulically isolating intervals in the annulus at locations adjacent the at least one ported assembly; flowing a first treatment fluid under pressure into the at least one isolated ported assembly to treat the formation in the isolated interval of the wellbore by pressurized treatment fluid flowing from the ported assembly; opening one or more flow diverter valves positioned uphole of the isolated assembly; and diverting the first treatment fluid from within the tubular member through the flow diverter valve, through the annulus to surface.

A further method is provided for treating a subteranian formation, the method comprising: inserting a tubular member into a wellbore intersecting the subterranean formation, the tubular member being adapted to receive a treatment fluid under pressure and comprising plurality of ported assemblies spaced at intervals along a length of the tubular member and one or more flow diverter valves positioned uphole of each of said ported assemblies; setting an isolation device to hydraulically isolate a first at least one interval in the annulus, said first at least one interval having at least one first ported assembly positioned therein; flowing treatment fluid under pressure through the first ported assembly and allowing treatment of the formation in the first isolated interval of the wellbore by the pressurized treatment fluid; releasing treatment fluid pressure; and repeating the steps of: i. opening one or more flow diverter valves positioned uphole of the isolated interval; ii. diverting treatment fluid from within the tubular member through the one or more flow diverter valves into the annulus uphole of the isolated interval, to equalize annular pressure above the isolated interval with annular pressure within the isolated interval; iii. initiating movement of tubular member to a subsequent interval of the wellbore, said subsequent interval comprising at least one subsequent ported assembly; iv. setting the isolation device to hydraulically isolate the subsequent at least one interval in the annulus; v. flowing treatment fluid under pressure through the at least one subsequent ported assembly to the formation in the isolated subsequent intervals of the wellbore by the pressurized treatment fluid; and vi. releasing treatment fluid pressure.

A method is further provided for treating one or more isolated intervals of a subteranian formation. The method comprises flowing treatment fluid under pressure through a first ported assembly on a tubular member and allowing treatment of the formation in a first isolated interval by the pressurized treatment fluid; moving the tubular member to a subsequent interval of the wellbore, said subsequent interval comprising at least one subsequent ported assembly; and simulataneously circulating treatment fluid from within the tubular member through one or more flow diverter valves into an annulus uphole of the first isolated interval while moving the tubular member.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, wherein:

FIGS. 1a to 1m illustrate in cross-section an environment and a method of fracing or treating a formation using a treatment string within a production casing according to an embodiment of the present invention;

FIG. 2 is an elevation view of a treatment string with a ported assembly and a flow diverter valve of the present invention; and

FIG. 3 is a process diagram illustrating a first method of the present invention;

FIG. 4 is a process diagram illustrating a second method of the present invention; and

FIG. 5 is a process diagram illustrating a third method of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Although the device and method of the present invention may be employed for various types of wells and completion procedures, such as with open hole packers in an uncemented well, a horizontal cemented well will be referred to herein for illustrative purposes.

With reference to FIGS. 1a to 1m , a production casing 16, also known as a completion string or wellbore liner, is inserted, or tripped, into the wellbore 10 to its terminus 11. An annular space 18, or annulus, is formed between the casing 16 and the wall of the wellbore 10. The production casing 16 may be considered a tubular member capable of flowing or communicating fluids under pressure along the wellbore.

Assemblies 20 are employed to join segments 17 of the production casing. Alternately, if no pipe segments are to be employed and the assemblies 20 are to be joined directly, then the assemblies 20 may have cooperative thread patterns, or alternate joining means.

The assemblies are preferably ported assemblies 20 having one or more ports 28. In some cases, the assemblies 20 are of the form of a “burstable disk”, also known as a “rupture disk” or “burst disk”. The disk has a rupture pressure threshold, and is located to block the flow of fluids through the hole while intact. Once the treatment fluid pressure reaches this threshold, the disk bursts to allow the treatment fluid to escape through the casing hole and fracture the formation strata.

Alternatively, some ported assemblies 20 provide a means of sealing a port 28 in a completion string from fluid flow therethrough when the insert is intact.

Further alternatively, the ported assemblies 20 may have shiftable sleeves that can be opened and closed by any number of means including, but not limited to hydraulic pressure acting on the sleeve or by mechanical actuation of an intervention tool that is deployed by coiled tubing, wireline or other means downhole to engage and move the sleeve to open the port 28.

A method of sequential fluid treatment of multiple intervals with a tubular member in a wellbore is now described. Cement is pumped down the production casing 16 and through each of the ported assemblies 20. The cement continues to be pumped until it exits the production casing near the wellbore terminus 11 and begins to fill the annulus 18, including around the collars 20 (FIG. 1e ). Pumping of the cement is accomplished with a tubular pumping member 112 that pushes the cement down the production casing until it reaches the terminus 11, at which point the cement has been largely evacuated from the production casing into the annulus past each of the ported assemblies 20 (FIG. 1f ). The operator can then slightly pressure-up the casing string to ensure all of the cement has been evacuated from the casing, sometimes referred to as “bumping up the wiper plug”. Once the cement sets to securely bond the production casing in the wellbore, the well is ready to be completed.

Completion of the well requires, in this example, a coil fracturing or treatment system where a tubular member preferably in the form of a treatment string 114 is tripped down the production casing 16 (FIG. 1g ). The treatment string 114 is located so as to position an isolation device 106 in a manner which fluidly isolates a given interval 116 of the production casing.

Preferably a packer/cup or cup/cup type straddle system 106 is employed as the isolation device to isolate a first ported assembly 20 a, referred to herein as the first stage. A treatment fluid is then injected under pressure into the isolated interval 116 of the ported assembly. When a threshold pressure is reached, the treatment fluid exits through the first ported assembly 20 a to initiate the fracing or other treatment process. The fracing or treatment process continues in the vicinity of the first ported assembly 20 a as the pressurized treatment fluid (indicated by 119 in FIG. 1i ) exits the ports 28 and through the initial cracks to propagate further cracking 120 or to treat or stimulate the formation.

Once the fracing or treating process is completed for the first stage, the pressure on the treatment fluid is released and the treatment string is moved back to create a further isolated interval 120 straddling the a subsequent ported assembly 20 b (FIG. 1j ), and the above fracing or treating process is followed for this second stage. This process is repeated for each stage (FIG. 1k ) until the last stage (20 f in FIG. 1L) is completed and the treatment string is rigged out. The well is then ready for production by flowing the target fluid (14 in FIG. 1m ) from the formation through the many ports and up the production casing to surface.

A further preferred embodiment of the invention is illustrated in FIG. 2. In many fracking or stimulation situations, a first treatment fluid such as water is first pumped down the inner bore of the production string 114 and out through ported assemblies 20. The ported assemblies 20 are preferably isolated from other stages of the formation by an isolation device 106, preferably in the form of a cup/packer or cup/cup type straddle system 106, comprising an upper packer 106 a uphole of the ported assembly 20 and a lower packer 106 b downhole of the ported assembly 20, to ensure that the first treatment fluid is directed to the isolated stage 116 of the formation to be stimulated. The straddle system 106 seals against casing 16 to prevent fluid from flowing into the annulus 18 outside of the isolated stage 116. In a next step, a second treatment fluid, optionally sand followed by a fracking slurry, is pumped down the well to frac the formation. Alternatively, the second treatment fluid may be a non-fracking second stimulant.

The pumping of the second treatment fluid acts to displace the first treatment fluid, typically water, in the inner bore and dispel the first treatment fluid through the ported assembly 20 and into the formation. Since most treatment strings 114 can be several kilometers long, a significant amount of first treatment fluid is standing in the inner bore that must be displaced into the formation by the sand. This first fluid is essentially wasted.

To reduce and prevent wastage, the present invention provides one or more flow diverter valves 110 positioned uphole from the ported assembly 20 and the straddle system 106, that serve to divert the first treatment fluid standing in the inner bore of the production string 114 back up through the annulus 18 to surface where it can be collected and reused. The method is illustrated in FIG. 3.

In further embodiments, as illustrated in FIGS. 4 and 5, the present flow diverter valve 110 serves to recycle water or other treatment fluids standing in inside the treatment string 114 out to surface when the treatment string 114 is moved from one interval to be treated, to a subsequent interval.

By diverting treatment fluid into annulus 18 above upper packer 106 a, fluid pressure above the isolated stage 116 is equalized with pressure experienced below the upper packer 106 a, to release the packer 106 a so that the treatment string 114 can be moved.

A similar pressure equalizing can be created on either side of lower packer 106 b, by means of a bypass valve 200 located downhole of lower packer 106 b and which can be opened to allow treatment fluid circulation downhole of lower packer 106 b, to release lower packer 106 b and allow the treatment string 114 to move to the next interval. By equalizing pressure on either side of the straddle system 106, the straddle system 106 experiences less wear as it is moved with the treatment string 114 from interval to interval.

Circulating fluids through the flow diverter valve 110 simultaneously while moving the treatment string 114 between intervals saves significant time from traditional methods in which fluid flow must be completely stopped when moving between intervals, and then started up again.

Fluid pressure created by the flow diverter valve 110 further serves to maintaining sufficient pressure in the annulus 18 at surface to prevent fluid from the treated interval from migrating past the upper packer 106 a and up towards surface.

Opening of the bypass valve 200 advantageously serves to minimize swabbing effects that result when bottom hole pressure, that is pressure of the formation below the first isolated interval 116, is reduced below the formation pressure due to the effects of pulling the treatment string 114 uphole from one interval to the next. This pressure reduction can detrimentally allow for an influx of formation fluids into the wellbore. By opening bypass valve 200, treatment fluid can be directed downhole of lower packer 106 b to equalize pressure and maintain bottom hole pressure at or above formation pressure to prevent ingress of formation fluids in to the wellbore from the bottom.

With further reference to FIG. 2, each of the present flow diverter valves 110 is preferably comprised of an inner sleeve 109 and an outer sleeve 108. Each of the inner sleeve 109 and the outer sleeve 108 comprise one or more ports, one of the ports 107 of the outer sleeve 108 being visible in FIG. 2. During stimulation or fracking operations the one or more ports of the inner sleeve 109 are misaligned with the ports 107 of the outer sleeve 108, to thereby prevent water from exiting port 107. Instead water travels down the inner bore of treatment string 114 and exits through ported assemblies 20. When the treatment fluid is switched, for example from water to sand, or when treatment of a previously stimulated interval 116 is complete and the treatment string 114 is to be moved to the next interval to be isolated and treated, the inner sleeve 109 is shifted or rotated mechanically to align the one or more ports of the inner sleeve 109 with the one or more ports 107 of the outer sleeve 108. The mechanical actuation may take the form of the production string itself being moved, although other means of actuating the inner sleeve 109 would be obvious to a person of skill in the art and are included in the scope of the present invention.

At this point, standing water or other treatment fluids in the inner bore of the treatment string 114 are displaced and caused to exit port 107 and travel up the annulus 18 to the surface where it can be collected and reused.

As mentioned earlier, fluid flowing out of exit port 107 and travelling through annulus 18 to surface equalizes pressure on either side of the upper packer 106 a. this advantageously ensures that formation fluid from the treated interval 116 does not travel into the wellbore or up to surface.

More preferably, a metering device may optionally be applied to the treatment string 114 or to the casing 16 to measure the flow of fluids being recycled back to surface. The metering device provides flow data on the flow rate of fluids being recycled back to surface to help operators determine when all of the recycled fluid has been recovered and when to close the diverter valve 110 and resume normal operation. When the system is ready for treating an interval through the ported assembly 20, the inner sleeve 109 of the flow diverter valve 110 is shifted or rotated to misalign the one or more ports on the inner sleeve 109 with the one or more ports 107 on the outer sleeve 108, thereby preventing fluid flow through these ports. Hydraulic pressure in the treatment string 114 helps to maintain the diverter valve 110 in a closed position.

The above description is intended in an illustrative rather than a restrictive sense, and variations to the specific configurations described may be apparent to skilled persons in adapting the present invention to other specific applications. Such variations are intended to form part of the present invention insofar as they are within the spirit and scope of the claims below. 

We claim:
 1. A tubular member for treating a subterranean formation, the tubular member being insertable in a wellbore intersecting the subterranean formation and adapted to receive a treatment fluid under pressure, the tubular member comprising: a. at least one assembly having at least one port; b. a straddle system comprising an upper packer uphole of the at least one assembly and a lower packer downhole of the at least one assembly to isolate an annular interval adjacent the ported assembly between the tubular member and the wellbore; and c. at least one flow diverter valve positioned uphole from the upper packer for diverting fluid from within the tubular member through an annulus between the tubular member and the wellbore to surface.
 2. The tubular member of claim 1, wherein each of the one or more flow diverter valves comprises: an inner ported sleeve shiftable within an outer ported sleeve, wherein said inner ported sleeve is shiftable from a first position in which one or more ports on the inner ported sleeve are misaligned with one or more ports on the outer ported sleeve, to a second position in which one or more ports on the inner ported sleeve are aligned with one or more ports on the outer ported sleeve.
 3. The tubular member of claim 2, wherein the inner sleeve is shiftable by hydraulic pressure.
 4. The tubular member of claim 1, further comprising at least one bypass valve located downhole of the lower packer for circulating treatment fluid from within the tubular member through the annulus between the tubular member and the wellbore downhole of lower packer.
 5. A method for treating a subteranian formation, comprising: a. inserting a tubular member into a wellbore intersecting the subterranean formation, the tubular member being adapted to receive a treatment fluid under pressure and comprising at least one ported assembly and one or more flow diverter valves positioned uphole of said ported assembly; b. setting an isolation device in an annulus between the tubular member and the wellbore for hydraulically isolating intervals in the annulus at locations adjacent the at least one ported assembly; c. flowing a first treatment fluid under pressure into the at least one isolated ported assembly to treat the formation in the isolated interval of the wellbore by pressurized treatment fluid flowing from the ported assembly; d. opening one or more flow diverter valves positioned uphole of the isolated assembly; and e. diverting the first treatment fluid from within the tubular member through the flow diverter valve, through the annulus to surface.
 6. The method of claim 5, wherein diverting the first treatment fluid through the annulus to surface balances pressure around the isolation device and prevents egress of formation fluid from treated interval into the wellbore and up to surface.
 7. A method for treating a subteranian formation, the method comprising: a. inserting a tubular member into a wellbore intersecting the subterranean formation, the tubular member being adapted to receive a treatment fluid under pressure and comprising plurality of ported assemblies spaced at intervals along a length of the tubular member and one or more flow diverter valves positioned uphole of each of said ported assemblies; b. setting an isolation device to hydraulically isolate a first at least one interval in the annulus, said first at least one interval having at least one first ported assembly positioned therein; c. flowing treatment fluid under pressure through the first ported assembly and allowing treatment of the formation in the first isolated interval of the wellbore by the pressurized treatment fluid; and d. repeating the steps of: i. releasing treatment fluid pressure; ii. opening one or more flow diverter valves positioned uphole of the isolated interval; iii. circulating treatment fluid from within the tubular member through the one or more flow diverter valves into the annulus uphole of the isolated interval, to equalize annular pressure above the isolated interval with annular pressure within the isolated interval; iv. simultaneously moving the tubular member to a subsequent interval of the wellbore, said subsequent interval comprising at least one subsequent ported assembly; v. setting the isolation device to hydraulically isolate the subsequent at least one interval in the annulus; and vi. flowing treatment fluid under pressure through the at least one subsequent ported assembly to the formation in the isolated subsequent intervals of the wellbore by the pressurized treatment fluid.
 8. The method of claim 7, wherein the tubular member is moved downhole for treating the wellbore therebelow.
 9. The method of claim 7, wherein the tubular member is moved uphole for treating the wellbore thereabove.
 10. The method of claim 7, wherein diverting treatment fluid from within the tubular member through the one or more opened flow diverter valves prevents migration of fluid from the isolated treated interval up the annulus to surface.
 11. The method of claim 7, further comprising, prior to moving the tubular member: i. opening at least one bypass valve located downhole of the isolated interval; and ii. circulating treatment fluid from within the tubular member through the at least one bypass valve into the annulus downhole of the isolated assembly simultaneously while moving the tubular member, to equalizing annular pressure below the isolated interval with annular pressure within the isolated interval.
 12. A method for treating one or more isolated intervals of a subteranian formation, the method comprising: a. flowing treatment fluid under pressure through a first ported assembly on a tubular member and allowing treatment of the formation in a first isolated interval by the pressurized treatment fluid; b. moving the tubular member to a subsequent interval of the wellbore, said subsequent interval comprising at least one subsequent ported assembly; and c. simulataneously circulating treatment fluid from within the tubular member through one or more flow diverter valves into an annulus uphole of the first isolated interval while moving the tubular member. 